Abstract: A bus powered device includes a signal processing control circuit connected to and powered by a bus at a predetermined operating current and a bus current modulator circuit interconnected in series with a signal processing control circuit to the bus for providing a bipolar communication signal having an average current of substantially zero; the total series current of both the circuits is only the current required by the signal processing control circuit or the absolute value of the most negative current excursion during communication, whichever is greater.

Abstract: A variable length sensor probe system for connection to a sensor well includes a housing adapted for connection to the proximate end of a sensor well; a sensor probe having a distal end for contacting the distal end of the sensor well and a proximate end extending into the housing; and an indexing device for interconnecting the housing and the proximate end of the sensor probe for setting the penetration of said sensor probe in the sensor well at one of a number of discrete positions and continuously urging the distal end of the sensor probe against the distal end of the sensor well.